Endodontic dental instrument

ABSTRACT

The present invention is directed to improved endodontic dental instruments for extirpating and enlarging a root canal and methods for use thereof. The dental instruments of the invention include a helical radial land and a helical blade edge spaced from the land on its opposite sides by helical flutes. Dental instruments according to the invention exhibit improved and more balanced side cutting in curvilinear canals and non-circular canal areas such as fins or anastomosis canal regions.

FIELD OF INVENTION

The invention relates generally to the field of endodontics and moreparticularly to instruments and methods for extirpating and enlarging aroot canal.

BACKGROUND OF THE INVENTION

In the field of endodontics, one of the most important and delicateprocedures is that of cleaning or extirpating a root canal to provide aproperly dimensioned cavity while essentially maintaining the centralaxis of the canal. This step is important in order to enable completefilling of the canal without any voids and in a manner which preventsthe entrapment of noxious tissue in the canal as the canal is beingfilled.

In cleaning and enlarging the root canal, instruments called files orreamers are used. Commonly, both files and reamers have flutes whichspiral along a portion of the instrument length, and whether theinstrument is a file or a reamer is determined by the pitch of theflutes. A greater pitch enables the instrument to cut better in a rotarymode, hence a reamer, and a lesser pitch enables the instrument to cutbetter in the reciprocating mode, hence a file. During a cleaning andshaping operation performed with such a file or reamer, the instrumentis normally rotated and moved into and out of the root canal along thelongitudinal axis of the instrument.

A widely used type of file or reamer is known by the designation"K-file" or "K-reamer". These instruments are made from a tapered rodwhich may be triangular or square in cross-section. The instruments arefabricated from the rods by twisting the rod to form a generally helicalflute along the working portion of the rod, or the helical flute may bemachined into the shaft.

The K-type instruments have several disadvantages. First, theinstruments have a tendency to transport the central axis of a curvedcanal as the instrument cuts, mostly where the greatest pressure isexerted against the wall of the canal. Second, as the instruments arecontinuously rotated, the blades can become locked into the canalcausing the instrument to break.

Finally, when modifications are made on conventional files and reamersto limit the tendency of the instrument to act as a screw or to diminishcanal transportation, the tissue removal efficiency is generallysacrificed, particularly when a substantially non-circular canal isencountered as in a "fin" or "anastomosis."

It is therefore an object of the invention to provide an improvedendodontic dental instrument.

Another object of the invention is to provide an endodontic dentalinstrument which enables improved removal efficiency of material from aroot canal.

A further object of the invention is to provide an endodontic dentalinstrument having high tissue removal efficiency for non circular and/orcurved root canals in addition to generally straight, circular canals.

SUMMARY OF THE INVENTION

With regard to the above and other objects, the present invention isdirected to an endodontic dental instrument for use in extirpating andenlarging a root canal. The instrument comprises an elongate shankhaving a drive end and a tip end and preferably tapers toward the tipend. A working portion extends along at least a portion of the shankbetween the drive end and the tip end. The working portion includes atleast one helical radial land spaced from a helical blade edge by ahelical flute. Preferably, the land and blade edge spiral the workingportion at substantially the same pitch. In one embodiment, the workingportion is asymmetrical, that is, it includes a combination of a helicalbearing surface defined by a helical radial land and a helical bladeedge generally juxtaposed with respect to the land and spaced therefromby at least a pair of helical flutes located on opposite sides of theblade edge between the edge and the land.

By the claimed structure, the helical blade edge is urged into cuttingengagement to a greater degree than the helical land portion of the fileas the file is rotated in the canal. However, the blade edge is forcedto cut more equally on the inside and outside of the canal curvaturesthan conventional symmetric instruments which have a tendency to cutprimarily on only one side of a canal curvature due to the forcesimposed on the canal wall by the instrument when it is in bendingflexure.

The working portion therefore may include at least one helical radialland having helical flank edges which define a bearing surfacetherebetween, and at least one helical blade-like edge which, whenviewed in cross-section, is generally juxtaposed with the land.

In a further embodiment, the working portion may have two spaced aparthelical radial lands and a blade edge, all of which are spaced apartabout 120° viewed in cross-section, and the lands and blade edge havesubstantially the same pitch. Helical flutes subtend the lands and bladeedge.

In yet another embodiment, the working portion has three spaced-aparthelical radial lands when viewed in cross-section, each having helicalflank edges so as to define a helical bearing surface on each land, anda helical blade edge located between two of the lands.

In another embodiment, the working portion includes one or morespaced-apart helical blade edges terminating inwardly of the peripheryof the working portion, when viewed in cross-section, and a helicalradial land disposed between the blade edges. In a further embodimentthe working portion includes helical radial lands that intermittentlynarrow into blade edges and where both the lands and blade edges projectessentially the same distance from the central axis of the instrument.

Each embodiment of the invention is therefore characterized by a workingportion having one or more helical radial lands adjacent one or morehelical blade-like edges which may advance along the shank toward thetip at the same or a different pitch relative to the land or lands. Theland or lands may be continuous end-to-end or it or they may bediscontinuous, such as being interrupted by an additional helical fluteadvancing toward the tip end at a substantially different pitch,intersections of the additional flute with the land or lands defininghelically spaced apart sections of a blade-like edge. Therefore, theblade-like cutting edge or blade edges may also be continuous ordiscontinuous and may be adjacent the land or lands by virtue of havingbeen defined by one or more land/flute intersections along the workingportion.

The helical radial land or lands in the embodiments of the invention incombination with one or more helical blade edges enable improved cuttingefficiency and control, which is particularly evident in working curvedcanals and non-circular curved canals, providing more uniform andcomplete material removal. The helical radial land bears against thecanal surface to limit lateral transportation of the working portionrelative to the original canal axis, while causing the working portionto self-advance into fin or anastomasi areas of the canal missed byconventional instruments.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the invention will now be furtherdescribed in the following detailed description of various embodimentsin conjunction with the accompanying drawings in which:

FIG. 1 is an elevational view of an endodontic dental instrumentaccording to one embodiment of the invention;

FIG. 2 is a cross-sectional view of the endodontic dental instrument ofFIG. 1 taken along line 2--2 thereof;

FIG. 3 is a partial longitudinal view in section of the dentalinstrument of FIG. 1 taken along line 3--3 thereof;

FIG. 4 is an elevational view of an endodontic dental instrumentaccording to another embodiment of the invention;

FIG. 5 is a cross-sectional view of instrument of FIG. 4 taken along theline 5--5 of FIG. 4 thereof;

FIG. 6 is a partial sectional view of the instrument of FIG. 4 takenalong line 6--6 thereof;

FIG. 7 is an elevational view of an endodontic dental instrumentaccording to still another embodiment of the invention;

FIG. 8 is a cross-sectional view taken along the line 8--8 of FIG. 7;

FIG. 9 is a partial sectional view of the instrument of FIG. 7 takenalong line 7--7 thereof;

FIG. 10 is an elevational view of endodontic dental instrument accordingto yet another embodiment of the invention;

FIG. 11 is a cross-sectional view taken along the line 11--11 of FIG.10;

FIG. 12 is a partial sectional view of the instrument of FIG. 10 takenalong line 12--12 thereof;

FIG. 13 is an elevational view of an endodontic dental instrumentaccording to still another embodiment of invention;

FIG. 14 is a cross-sectional view taken along the line 14--14 of FIG.13; and

FIG. 15 is a partial sectional view of the instrument of FIG. 13 takenalong line 15--15 thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The figures illustrate dental instruments having various working portionconfigurations within the scope of the appended claims which may be usedas a file or reamer for removing material from the root canal of atooth. Referring first to FIGS. 1--3, there is shown a file generallydenoted as 10 having a head portion 12 at its proximal end and ashank-like working portion 14, which is preferably tapered, extendingalong at least a portion of the length of the file 10 and asubstantially cylindrical dome-end pilot 16 at the distal end. Thecylindrical pilot 16 is well known and more fully described in U.S. Pat.No. 4,332,561 to McSpadden, incorporated herein by reference as if fullyset forth. The pilot 16 is preferred, but is not required.

The head or driving end 12 of the file 10 contains a fitting portion 13formed in the upper portion of the head for mating with a chuck of adental handpiece (not shown). Alternately, or in addition to the fitting13, the head 12 may include a knurled or otherwise treated surface tofacilitate hand manipulation of the file 10.

The working portion 14 is comprised of one or more blade-like helicalcutting edges 22 and one or more helical radial lands 18 (one each inthe embodiment of FIG. 1). In the illustrated embodiment, helical flutes20a and 20b subtend blade edge 22, and land 18. That is, flute 20a isspaced about 90° from flute 20b so as to define helical radial land 18opposite the blade edge 22 which lies between flutes 20a and 20b at theperiphery of the working portion 14 so that the flutes 20a and 20bsubtend each side of the land 18 and the edge 22.

As shown in FIG. 2, blade edge 22 is generally opposite a bearingsurface 19 of radial land 18. A used herein, A "radial" in connectionwith the lands means that the bearing surface 19 of the land 18 iscurvilinear as opposed to flat, when viewed in cross-section. The wallsof flutes 20a and 20b intersect the periphery of the working portion 14in regions denoted by the letters A, B and C immediately adjacent theshank periphery at an angle of about 90 degrees to tangent to form whatis commonly referred to as a zero or neutral rake angle from theperspective of the surfaces of the flutes 20a and 20b. For purposes ofthis invention, the rake angle can be neutral, positive or negative butis preferably about neutral.

It will be appreciated that radial land 18 presents bearing surface 19between land flank edges 18a and 18b (FIGS. 2 and 3) so that whenrotated in a canal in a counterclockwise direction, only flank edge 18bcuts while surface 19 bears against the canal wall. Land flank edges 18aand 18b are located at the periphery of the working portion 14 onopposing sides of the bearing surface 19 of radial land 18. Blade edge22 also lies at the periphery of the working portion between flutes 20aand 20b, and is about 180° from the bearing surface 19.

FIGS. 4-6 illustrate another embodiment of an endodontic dentalinstrument 10' according to the invention. In this embodiment, threeflutes subtend a radial land and blade-like cutting edges in a workingportion 25. As shown in FIG. 5, a first flute 26a and a third flute 26care on opposite sides of helical radial land 28. Flutes 26a and 26b areon opposite sides of a blade edge 30a and flutes 26b and 26c are onopposite sides of a blade edge 30b. Flute 26b is generally opposite abearing surface 32 of land 28.

The walls of flutes 26a, 26b and 26c intersect the periphery of theworking portion 25 immediately adjacent the shank periphery at an angleof about 90 degrees. Blade edges 30a and 30b are nominally about 90°apart.

Land flank edges 28a and 28b lie on the periphery of the working portion25 on opposing sides of the bearing surface 32 of land 28. Helicalblade-like cutting edges 30a and 30b and land flank edges 28a and 28bare therefore subtended by flutes 26a, 26b and 26c and lie at theperiphery of the working portion 25. In counterclockwise rotation, onlyland flank edge 28a provides a cutting edge.

Thus, according to this embodiment, there are at least three helicalflutes with a helical radial land between two of the flutes andblade-like cutting edges between two pairs of the flutes with the bladeedges spaced apart about 90° and each spaced about 130° from an adjacentland flank edge, such that in cross section there is one land and threeflutes, providing another embodiment of an asymmetrical working portion25 according to the invention.

Yet another embodiment of an endodontic instrument 10" according to theinvention is illustrated in FIGS. 7-9. In this embodiment, twocontinuous helical radial lands 36A and 36B are formed in and along aworking portion 38 of the dental instrument 10". As shown in FIG. 8,helical land 36A originates nominally about 120° from helical land 36Bsuch that helical lands 36A and 36B are subtended by a helical flute40b. There are two helical flutes 40a and 40c subtending each side of ablade-like cutting edge 42 and lands 36B and 36A, respectively.

Flutes 40c and 40b are on opposite sides of a bearing surface 44 of land36A. Flutes 40b and 40a are on opposite sides of bearing surface 46 ofland 36B. The walls of flutes 40a, 40b and 40c intersect the peripheryof the working portion 38 immediately adjacent the shank periphery at anangle of about 90 degrees to tangent of the shank periphery.

FIG. 9 illustrates land flank edges 36a and 36b on the shoulders of land36A and land flank edges 36c and 36d on the shoulders of land 36B.During clockwise rotation of the instrument, flank edges 36b and 36cprovide cutting edges.

Blade edge 42 between helical flutes 40a and 40c is also illustrated.All of the edges 42, 36a, 36b, 36c, and 36d are located on the peripheryof the working portion 38. According to this embodiment, there are thusprovided three helical flutes separated by two lands and a blade-likecutting edge with the lands spaced apart nominally about 120° and theblade edge spaced about 120° from the lands between the lands, providingan asymmetrical working portion according to the invention.

FIGS. 10-12 illustrate still another endodontic instrument 10"'according to the invention. In this instrument, there are four helicalflutes 50a, 50b, 50c and 50d and one helical radial land 52 between eachset of four helical flutes formed in and along an asymmetrical workingportion 54 of the dental instrument. The helical flutes subtend helicalblade-like cutting edges 56a, 56b and 56c and land flank edges 52a and52b of land 52. In counter-clockwise rotation of the instrument, flankedge 52b is a cutting edge.

Blade edge 56b is at the periphery of the working portion 51 andopposite helical radial land 52. In this embodiment, blade edges 56a and56c do not extend to the periphery of the working portion, but terminateat a point which is spaced inwardly of the circumference of theperiphery defined by bearing surface 58 and blade edge 56b.

The relationship of blade edges 56a, 56b and 56c is best seen in FIG.11. Blade edge 56a is between flutes 50a and 50b, blade edge 56b isbetween flutes 50b and 50c and blade edge 56c is between flutes 50c and50d. Flutes 50a and 50d each are on opposite sides of a bearing surface58 of land 52. One side of the wall of each of flutes 50a, 50b, 50c and50d intersects the periphery of the working portion 54 immediatelyadjacent the shank periphery at an angle of about 90 degrees to tangentof the shank periphery. The other sides of the walls of flutes 50a, 50b,50c and 50d terminate at blade edges 56a and 56c spaced inwardly of thecircumference of the periphery of the working portion 54 as defined bybearing surface 58 and blade edge 56b.

Thus, according to this embodiment, the instrument includes four helicalflutes with one helical radial land, two of the flutes merging toprovide a blade-like cutting edge adjacent the periphery spaced about180° from the land, and opposed pairs of intersecting flutes merging toprovide blade-like cutting edges also about 180° apart from one anotherspaced inwardly of the periphery and shifted nominally about 90°relative to the land, the arrangement providing an asymmetrical workingportion according the invention.

A further endodontic instrument 10'" according to the invention isillustrated in FIGS. 13-15. In this instrument, three helical radiallands 60A, 60B and 60C and four helical flutes 62a, 62b, 62c and 62d areprovided in and along the working portion 64. The helical flutes 62c and62d subtend each side of blade-like cutting edge 66 and lands 60C and60A, the edge 66 lying at the periphery of the working portion 64 andopposite helical land bearing surface 68 of helical land 60B. All of thehelical lands and the blade edges in this embodiment extend to theperiphery of the working portion 64.

The relationship of blade-like cutting edge 66 and lands 60A, 60B and60C is best seen in FIG. 14. As shown, blade edge 66 is between flutes62c and 62d whereas bearing surface 68 of helical land 60B is betweenflutes 62a and 62b spaced from edge 66 about 180°. Bearing surface 70 ofhelical land 60C is between flutes 62b and 62c, and bearing surface 72of helical land 60A is between flutes 62d and 62a. The walls of flutes62a, 62b, and 62c directed toward lands 60A, 60B, and 60C intersect theperiphery of working portion 14 immediately adjacent the shank peripheryat an angle substantially less than about 90 degrees to tangent of theshank periphery. The walls of flutes 62c and 62d directed toward edge 66intersect the shank periphery at an angle nominally of about 90°.

As shown in FIG. 15, flank edges 60a₁, 60a₂, 60b₁, 60b₂, 60c₁, and 60c₂are on the shoulders of lands 60A, 60B and 60C, respectively. All ofthese land flank edges are located on the periphery of the workingportion 64. In clockwise rotation of the instrument, flank edges 60a₂,60b₂, and 60c₂ provide cutting edges According to this embodiment, thereare three helical radial lands and a blade-like edge all spaced-apartnominally about 90° and four helical flutes separating the lands and theblade edge to provide a working portion according to the invention.

The endodontic instruments of the invention provide improved removal ofmaterial in the root canal of a tooth due to the combination of helicalcutting blades and bearing surfaces along the working portion.Accordingly, the endodontic instruments of the invention have been foundto have improved side cutting capability and an inherent propensity towork into canal areas that are noncircular so as to remove material fromanastomosi previously untouched or insufficiently worked by conventionalinstruments, as well as move evenly working curvilinear canals.

The endodontic instruments of the invention may be used by manipulatingthe file manually in a rotating/reciprocating action, or the file orreamer may be manipulated by attaching the instrument to a motorizeddevice for effecting the removal of material from the root canal. Asdepicted in the foregoing illustrations the working portion extends asubstantial distance along the length of the instrument and may possessa generally tapered configuration as a path is traced from the drive endof the working portion to the tip end. The diameter of the workingportion may increase from about 0.01 to about 0.07 mm, preferably about0.02 mm, for each millimeter up the working portion from the tip end tothe drive end. The entire working portion of the shank may be about 20to 30 mm, but longer or shorter working portions may be used. Thediameter of the working portion adjacent the tip end may range fromabout 0.08 to about 1.9 millimeters.

The rake angles of the blade edges may be positive, negative, orneutral, but are preferably about neutral with respect to the peripheryof the working portion. In order to make the instruments having thedesired rake angles, the instruments may be ground from a straight ortapered rod, twisted and/or drawn to a taper with or without grinding.

The endodontic instruments of the invention are preferably made formsurgical stainless steel, however, they can also be made from compositematerials such as nickel titanium or other "exotic" alloys, and thelike. The preferred material for the instruments of the invention isnickel titanium or titanium 13--13. Those of ordinary skill willrecognize that techniques for making conventional instruments maygenerally be applied to the manufacture of instruments according to theinvention and with various known or later-developed materials. Suitablegrinding techniques which may be used are described in metallurgicaltexts for grinding metals. For example, it is known that certaingrinding wheels or bits for making instruments out of one material maynot be effective for other or different materials. While a grindingsurface made of course grit and rotating at a relatively high speed maybe suitable for grinding stainless steel or a hard metal shaft, anickel-titanium shaft may require a finer grit grinding surface rotatingat a relatively slower speed in order to effectively abrade the shaft toform the necessary edges and lands.

The foregoing detailed description is given for understanding of theinvention and to illustrate its various features and known advantages,but no unnecessary limitations are to be understood therefrom.Modifications of the various illustrated embodiments and, indeed, thefashioning of other or even improved embodiments, some of which may beobvious to those skilled in the art upon reading the disclosure, may bemade without departing from the spirit and scope of the invention asdefined by the appended claims.

What is claimed is:
 1. An endodontic dental instrument for extirpatingand enlarging a wall of a root canal which comprises an elongate shankhaving a drive end and a tip end with a working portion defined along atleast a portion of the length of the shank between the tip end and thedrive end, the working portion including a helical radial land and ahelical blade edge having substantially no land with a first helicalflute disposed between said land and said helical blade edge on one sideof said blade edge and a second helical flute disposed between saidhelical blade edge and said land on the other side of said blade edge.2. The instrument of claim 1 wherein the shank tapers from a pointadjacent the drive end to a point adjacent the tip end.
 3. Theinstrument of claim 1 wherein the land defines a curvilinear bearingsurface which provides, with respect to at least one direction ofrotation of the shank about its longitudinal axis, a leading helicalblade edge on the land and a trailing helical edge with the bearingsurface therebetween, the blade edge being ahead of the leading edge andspaced therefrom by said first flute.
 4. The instrument of claim 3wherein said shank is tapered from a point adjacent said drive end to apoint adjacent said tip end.
 5. The Instrument of claim 1 wherein thefirst and second helical flutes span completely between said blade edgeand said land.
 6. The instrument of claim 1 wherein said second helicalflute subtends said helical radial land and said helical blade edge onone side of said blade edge and said first helical flute subtends saidhelical land and said helical blade edge on an opposing side of saidblade edge.
 7. The instrument of claim 1 further comprising a secondhelical blade edge spaced from said blade edge by said second helicalflute and a third helical flute disposed between said second helicalblade edge and said radial land.
 8. The instrument of claim 1 furthercomprising a second helical radial land spaced from said land by a thirdhelical flute and a fourth helical flute disposed between said secondhelical land and said helical blade edge.
 9. The instrument of claim 1further comprising a second helical blade edge spaced from said bladeedge by a third helical flute and a fourth helical flute disposedbetween said second blade edge and said radial land.
 10. The instrumentof claim 9 further comprising a third helical blade edge spaced fromsaid second blade edge by a fifth helical flute wherein said fourthhelical flute separates said second helical blade edge from said thirdhelical blade edge and said fifth helical flute separates said thirdhelical blade edge and said helical radial land.
 11. The instrument ofclaim 1 wherein the pitch of any of one of said blade edges is differentform the pitch of any one of said radial lands.
 12. The instrument ofclaim 1 wherein a second helical flute is disposed at a pitch differentfrom that of said first helical flute so as to intersect both saidhelical land and said helical flute at successive spaced apartintersections to define by said intersections a helically disposed,spaced apart series of segments of a generally helically arranged bladeedge having at least a radial component.
 13. An endodontic dentalinstrument for extirpating and enlarging a wall of a root canal whichcomprises an elongate shank having a drive end and a tip end with aworking portion defined along at least a portion of the length of theshank between the tip end and the drive end, the working portionincluding a helical radial land and a helical blade edge with a firsthelical flute disposed between said land and said helical blade edge onone side of said blade edge and a second helical flute disposed betweensaid helical blade edge and said land on the other side of said bladeedge and further comprising a second helical blade edge spaced from saidblade edge by a third helical flute and a fourth helical flute disposedbetween said second blade edge and said radial land wherein at least oneof said helical blade edges terminates radially inwardly of an adjacentblade edge.
 14. The instrument of claim 13 wherein the pitch of any ofone of said blade edges is different form the pitch of any one of saidradial lands.
 15. The instrument of claim 13 wherein said shank istapered from a point adjacent said drive end to a point adjacent saidtip end.
 16. An endodontic dental instrument for extirpating andenlarging a wall of a root canal which comprises an elongate shankhaving a drive end and a tip end with a working portion defined along atleast a portion of the length of the shank between the tip end and thedrive end, the working portion including a helical radial land and ahelical blade edge with a first helical flute disposed between said landand said helical blade edge on one side of said blade edge and a secondhelical flute disposed between said helical blade edge and said land onthe other side of said blade edge and a second helical blade edge spacedfrom said blade edge by a third helical flute and a fourth helical flutedisposed between said second blade edge and said radial land and a thirdhelical blade edge spaced from said second blade edge by a fifth helicalflute wherein said fourth helical flute separates said second helicalblade edge from said third helical blade edge and said fifth helicalflute separates said third helical blade edge and said helical radialland wherein at least one of said helical blade edges terminatesradially inwardly of an adjacent blade edge.
 17. The instrument of claim16 wherein the pitch of any of one of said blade edges is different formthe pitch of any one of said radial lands.
 18. The instrument of claim17 wherein said shank is tapered from a point adjacent said drive end toa point adjacent said tip end.